In recent years, as the traffic increases, it is desired to increase the bandwidth of the circuit (line) and achieve higher functionality of the network in the undersea cable system. Therefore, techniques such as OADM (Optical Add-Drop Multiplexer) and ROADM (Reconfigurable Optical Add-Drop Multiplexer) are applied to the undersea cable system.
In the undersea ROADM system, a Wavelength Division Multiplexing (WDM) communication is used, and, for example, a transmission apparatus inputs a client signal as a wavelength multiplexed optical signal into an undersea cable, and multiple paths are accommodated in a single optical fiber, so that the flexibility of the network is improved.
In the undersea cable system having the OADM function, the total power of the signal transmitted in the cable constituted by an optical fiber is configured to be at a constant level, and in a case where some of the wavelength component of the signal is lost because, e.g., the cable is disconnected, the other wavelength components of the signal is amplified, so that the total power of the signal is maintained at a constant level.
However, when the power of only a particular wavelength component of the signal is increased, and the power becomes equal to or more than a predetermined value, a change occurs in the optical spectrum because of, e.g., degradation of the waveform of the signal due to nonlinear effect of the optical fiber, and the transmission quality of the signal is degraded.
An optical communication system described in PTL 1 relates to a technique for ensuring the communication quality by correcting the total power of the signal with dummy light in a case where a fault occurs in a cable. In the optical communication system described in PTL 1, a terminal apparatus (optical transmission apparatus) includes a dummy light generation unit generating dummy light according to a portion where optical signal disconnection occurs, so that the strength (the power) of the transmitted signal is maintained at a constant level, in a case where a fault of cable disconnection occurs.